1. Field of the Invention
The present invention relates to a control device for a copier of the type loaded with a recyclic document feeder (RDF) and operable in a two-sided copy mode in which paper sheets each carrying an image on one side thereof are sequentially stacked in the copier and refed for transferring images on the other side thereof to produce two-sided copies.
2. Discussion of the Background
Modern copiers are operable with a RDF or an automatic document feeder (ADF) for automatically feeding documents one by one to promote efficient copying operations. The RDF feeds a document from a document tray to a glass platen and, after the document has been copied, returns the document to the tray to allow it to be fed again. In contrast, the ADF usually does not return a document once fed to the glass platen to a document tray. Concerning a single copy of documents, therefore, both the RDF and the ADF are operated in the same manner, i.e., they feed documents one by one for copying them and, on sensing the last document, they terminate the copying operations.
When two or more copies of documents are desired, the ADF and RDF each is operated in a particular way. Assuming that N (equal to or greater than 2) copies are desired, the ADF feeds one of the documents to the glass platen, scans the document N consecutive times, discharges the document, and then scans the next document N consecutive times. In this manner, the copying operation is repeated N times with each of the documents. On the other hand, the RDF feeds one document to the glass platen, scans the document once, returns it to the document tray, and then repeats such a procedure with all of the remaining documents to produce a single copy of the documents at a time. This is repeated N consecutive times to complete N copies of the documents. The RDF is advantageously applicable to a copier having a stapler or similar finisher because it produces a single copy of documents at a time.
The operations of the ADF and RDF are further different from each other when it comes to a copier operable in a two-sided copy mode. Specifically, the ADF products two-sided copies of documents by reproducing the first page N consecutive times while sequentially stacking the resulting one-sided copies on the intermediate tray, refeeding the one-sided copies from the tray to reproduce the second page on the other side thereof, stacking N copies of the third page on the tray, and so forth. On the other hand, the RDF feeds documents one by one while scanning only every two documents, i.e., copies only the odd pages and sequentially stacks then on the intermediate tray. When the documents are fed a second time, paper sheets are fed from a paper feeding device for the odd pages while the one-sided copies existing on the intermediate tray are refed for the even pages. More specifically, in this operation mode, paper sheets are fed from the intermediate tray and the paper tray alternately one at a time.
In the copier with the conventional RDF, a one-sided copy is refed from the intermediate tray for transferring an image to the other side substantially at the same time as a paper sheet fed from the paper feeding device and provided with an image on one side thereof enters the intermediate tray. Generally, the entry of a one-sided copy in and the refeed of a one-sided copy from the intermediate tray differ from one paper size to another with respect to timing. It is likely, therefore, that the entry and the refeed are disturbed unless they are effected in matching relation to the paper size, preventing desired two-sided copies from being achieved.